code: def test_str_cat_result_is_a_string(no_nulls_df):
      """
      Test wrapper for Pandas `.str.cat()` method
      when the outcome is a string.
      """
  
      result = no_nulls_df.process_text(
          column_name="text",
          string_function="cat",
      )
  
      expected = no_nulls_df.assign(text=no_nulls_df["text"].str.cat())
  
      assert_frame_equal(result, expected)
  
imports: import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 14 for calling a global function with example usage: test_str_cat_result_is_a_string(no_nulls_df) without return types